#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/ioctl.h>
#include <string.h>
#include <cutils/log.h>
#include <cutils/atomic.h>
#include <errno.h>

#include <sys/mman.h>

#define NUM_BUFFERS 2

inline size_t roundUpToPageSize(size_t x) {
    return (x + (PAGE_SIZE-1)) & ~(PAGE_SIZE-1);
}

int main()
{
	char const * const device_template[] = {
            "/dev/graphics/fb%u",
            "/dev/fb%u",
            0 };

    int fd = -1;
    int i=0;
    char name[64];

    while ((fd==-1) && device_template[i]) {
        snprintf(name, 64, device_template[i], 0);
        fd = open(name, O_RDWR, 0);
        i++;
    }
    
    if (fd < 0)
        return -errno;

    struct fb_fix_screeninfo finfo;
    if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)
        return -errno;

    struct fb_var_screeninfo info;
    if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
        return -errno;

    info.reserved[0] = 0;
    info.reserved[1] = 0;
    info.reserved[2] = 0;
    info.xoffset = 0;
    info.yoffset = 0;
    info.activate = FB_ACTIVATE_NOW;

    /*
     * Request NUM_BUFFERS screens (at lest 2 for page flipping)
     */
    info.yres_virtual = info.yres * NUM_BUFFERS;

    if (ioctl(fd, FBIOPUT_VSCREENINFO, &info) == -1) {
        info.yres_virtual = info.yres;
        printf("FBIOPUT_VSCREENINFO failed, page flipping not supported\n");
    }

    if (info.yres_virtual < info.yres * 2) {
        // we need at least 2 for page-flipping
        info.yres_virtual = info.yres;
        printf("page flipping not supported (yres_virtual=%d, requested=%d)\n",
                info.yres_virtual, info.yres*2);
    }

    if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1)
        return -errno;

    uint64_t  refreshQuotient =
    (
            (uint64_t)( info.upper_margin + info.lower_margin + info.yres )
            * ( info.left_margin  + info.right_margin + info.xres )
            * info.pixclock
    );

    /* Beware, info.pixclock might be 0 under emulation, so avoid a
     * division-by-0 here (SIGFPE on ARM) */
    int refreshRate = refreshQuotient > 0 ? (int)(1000000000000000LLU / refreshQuotient) : 0;

    if (refreshRate == 0) {
        // bleagh, bad info from the driver
        refreshRate = 60*1000;  // 60 Hz
    }

    if ((int)(info.width) <= 0 || (int)(info.height) <= 0) {
        // the driver doesn't return that information
        // default to 160 dpi
        info.width  = ((info.xres * 25.4f)/160.0f + 0.5f);
        info.height = ((info.yres * 25.4f)/160.0f + 0.5f);
    }

    float xdpi = (info.xres * 25.4f) / info.width;
    float ydpi = (info.yres * 25.4f) / info.height;
    float fps  = refreshRate / 1000.0f;

    printf(   "using (fd=%d)\n"
            "id           = %s\n"
            "xres         = %d px\n"
            "yres         = %d px\n"
            "xres_virtual = %d px\n"
            "yres_virtual = %d px\n"
            "bpp          = %d\n"
            "r            = %2u:%u\n"
            "g            = %2u:%u\n"
            "b            = %2u:%u\n",
            fd,
            finfo.id,
            info.xres,
            info.yres,
            info.xres_virtual,
            info.yres_virtual,
            info.bits_per_pixel,
            info.red.offset, info.red.length,
            info.green.offset, info.green.length,
            info.blue.offset, info.blue.length
    );

    printf(   "width        = %d mm (%f dpi)\n"
            "height       = %d mm (%f dpi)\n"
            "refresh rate = %.2f Hz\n",
            info.width,  xdpi,
            info.height, ydpi,
            fps
    );


    if (ioctl(fd, FBIOGET_FSCREENINFO, &finfo) == -1)
        return -errno;

    if (finfo.smem_len <= 0)
        return -errno;

    /*
     * map the framebuffer
     */

	int j = 0;
    while (info.yres_virtual > 0) {
    	printf("Try %d\n", j++);
    
        size_t fbSize = roundUpToPageSize(finfo.line_length * info.yres_virtual);
        void* vaddr = mmap(0, fbSize, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        if (vaddr != MAP_FAILED) {
            memset(vaddr, 0, fbSize);
            printf("OK\n");
            return 0;
        }

        printf("Error mapping the framebuffer (%s)\n", strerror(errno));

        info.yres_virtual -= info.yres;
        printf("Fallback to use fewer buffer: %d\n", info.yres_virtual / info.yres);
        if (ioctl(fd, FBIOPUT_VSCREENINFO, &info) == -1)
            break;
    }

    return 0;
}
